subject: Depth Analysis Of Plc Technology - Programmable Logic Controller, And Technology - Electrical [print this page] I. PLC Technical factors 1. Power line network unit (PNU)
It is responsible for controlling the power line network and distribution network from the unit if service integration. Through appropriate trunk interfaces telecommunications, PNU Call then spread to the feed network. Feed network according to the use of different media, PNU also converted from Low Call the data distribution network.
2. Power supply Line network terminal (PNT)
It to the end-user PC or Other Provide the appropriate interface, such as Ethernet or USB. To reduce costs, the self and the PC or other device to integrate.
3. Coupled device (CouplingUnit) It is the incoming line signal and filter noise. Currently, it is a pin inserted electrical socket device independent, in the future it may be and PLC Modem integrated in one. PLC modem and PC coupling devices within the collection of the day will allow PC can run directly on the web.
Distribution network is a shared medium, that is all connected users are sharing the same cable. In a typical urban configuration, it is transformed with a Transformer Connected to about 100 to 200 users. PLC system can best transfer rate in the 1Mbps to support 80 users, this percentage is enough. Technical support to customers by the PLC needs to have a technical condition, has a strong capacity bandwidth allocation medium access control (MAC) layer. This makes the power line network is not only able to support 80 I
Nternet users to exchange data back and forth, and can flexibly adapt to different rates of transmission of uplink and downlink data.
Second, the data signal transmission technology
1, Digital Spread Spectrum Technology (SST)
In the current practice, in order to achieve financial products for the home or the communication and control network, needs a more reliable multi-user environment, PL communications technology, spread spectrum carrier communication technology is adopted.
Spread spectrum communication relative to the narrow-band communications is concerned with certain technical advantages, mainly in anti-disturbance. Because the spread spectrum carrier signal bandwidth is usually larger (tens to hundreds of KHz), so its frequency interference reduced the relative proportion, in other words, is all kinds of noise can only affect a small part of the desired transmission of signals, and most of the signals are able to complete the correct destination, so for all types of interference has a strong resistance. The most common impulse noise, while the narrow-band communications receiver with a narrow pass band, so only a small part of the noise can enter the receiver, but such a receiver in the filter with high quality factor, instant the impulse noise will make it happen from the interference caused by its transmission to the signal generator misoperation; the use of low quality factor of the filter passband bandwidth, it will increase so that more noise into the receiver, so narrow Communication on the poor resistance to impulse noise.
Use of spread spectrum technology, however, received with great energy when the noise signal, the receiver will arrive the noise of high-energy part of the automatic stop working, so the receiver only affected a small portion of the signal error correction decoding it; In addition, the spread spectrum receiver using the filter device has a lower quality factor, and thus will not cause the system from interference, so the spread-spectrum technology is robust to noise.
General, there are currently three ways to achieve spread spectrum: the direct-sequence modulation, frequency hopping carrier and the carrier frequency of use of Chirps scanning.
This technology is the signal energy is distributed evenly in the whole band, and through the pseudo-random sequence to double the data stream to enable the signal to spread spectrum, this sequence several times in the transmission signal with binary data bit rate of the symbol rate.
